The present invention concerns a method and a system for determination of the feeding speed when cutting a workpiece by a bandsaw. The invention also concerns a computer program which can be used when employing the method and realizing the system.
Bandsaws are today used to a large extent in industry for cutting of metal bars. It is then of great importance that the cutting data are determined in an optimal way. In this case, cutting data means choice of tool type, such as tooth material and tool geometry, band velocity, tooth pitch, feeding or penetration speed, and cutting time. If non-optimal cutting data are chosen it will result in shorter band durability, non-flat cutting, rough cut surface, tooth fractures, uneconomic cutting, etc.
The most commonly occurring method to determine cutting data in industry today is based on the cross section area of the workpiece. For each material, a suitable cutting speed has been determined from experience. A typical determination of cutting data can today be performed in the following way.
A stainless steel (SS 2343) bar with a diameter of 100 mm is to be cut. Looking in a simple table one can find that SS 2343 should be cut with a cutting speed of 25 to 35 cm2/min. With some effort the minimum cross section of the bar is calculated as A=πr2=78 cm2 and the minimum cutting time is then calculated as 78/35 to 78/25=2.23 to 3.24 min. There are certain developed versions of this method—e.g. different cutting speeds can be given depending on the diameter of the bar.
These calculations include weaknesses since a number of factors are omitted, such as the width of the bandsaw blade, the hardness of the workpiece material and the condition of the sawing machine, etc. The most important omission, however, is that there is no reference to the shape of the cross section.
Suppose that a first customer cuts through a 100 mm thick bar, a second customer cuts a tube with 200 mm external diameter and 174 mm internal diameter, and a third customer cuts a slab with 300 mm×38 mm rectangular section. The workpieces of all three customers have the same cross-sectional area of 78 cm2 and would according to the present method of determination be cut with a cutting time of 2.23 to 3.2 min. Obviously, the customers would need a much more improved method of determining the cutting data to be used.
The aim of the present invention is to remedy the above-mentioned disadvantages in determining the cutting data for band sawing.